Around half of straight men and women potentially carry so-called homosexuality genes that are passed on from one generation to the next, according to new research.

This has helped homosexuality exist among humans throughout history, even though gay men tend to have fewer descendants who directly inherit their genes.

The researchers came to this conclusion using a computational model that, among others, included aspects of heredity and the tendency of homosexual men to come from larger families.

Around half of all straight men and women potentially carry so-called homosexuality genes that are passed on from one generation to the next. This has helped homosexuality to exist among humans throughout history, even though homosexual men tend to not have many descendants who can directly inherit their genes

However, the researchers did not identify any specific genes and instead the conclusions are based on the fact homosexuality must have a hereditary element.

This idea is reported by Giorgi Chaladze of the Ilia State University in Georgia, and published in Springer's journal Archives of Sexual Behaviour.

According to previous research, sexual orientation is influenced to a degree by genetic factors and is therefore heritable.

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Chaladze said this poses a problem from an evolutionary perspective, because homosexual men tend not to have many offspring to whom they can provide their genetic material.

THE CLAIMS OF A 'GAY GENE'

According to previous research, sexual orientation is influenced to a degree by genetic factors and is therefore heritable.

This poses a problem from an evolutionary perspective, because homosexual men tend to have fewer offspring to whom they can pass on their genetic material.

Other reports also suggest many heterosexual men are carriers of the genes that could predispose someone to homosexuality.

Based on the researcher's calculations, male homosexuality is maintained in a population at low and stable frequencies if half of the men and roughly more than half of the women carry genes that predispose men to homosexuality.

In fact, they have on average five times fewer children than their heterosexual counterparts.

Chaladze used an individual-based genetic model to explain the stable, yet persistent, occurrence of homosexuality within larger populations.

He took into account findings from recent studies that show that homosexual men tend to come from larger families.

These suggest the genes responsible for homosexuality in men increase based on the number of children someone has.

And this applies to large families that have both sons and daughters, because females also carry the genes.

Other reports also suggest many heterosexual men are carriers of the genes that could predispose someone to homosexuality.

Based on Chaladze's calculations, male homosexuality is maintained in a population at low and stable frequencies if half of the men and roughly more than half of the women carry genes that predispose men to homosexuality.

According to previous research, sexual orientation is influenced to a degree by genetic factors and is therefore heritable but this poses a problem from an evolutionary perspective, because gay men tend to have fewer offspring to whom they can pass on their genetic material

'The trend of female family members of homosexual men to have more offspring can help explain the persistence of homosexuality, if we also consider that those males who have such genes are not always homosexuals,' explained Chaladze.

The possibility that many heterosexual men are carriers can also explain why estimates of the number of men who have reported any same-sex sexual behaviour and same-sex sexual attraction are much higher than estimates of those who self-identify as homosexual or bisexual.

According to Chaladze, non-homosexual male carriers might sometimes manifest interest in homosexual behaviour without having a homosexual identity.

The possibility that a large percentage of heterosexual people are carriers of genetic material predisposing to homosexuality has implications for genomic studies.

Researchers should therefore consider including participants who do not have homosexual relatives in such studies.